A typical electrophotographic or electrostatographic reproduction machine employs a photoconductive member that is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive member selectively dissipates the charge thereon in the irradiated areas to record an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document.
After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the electrostatic latent image is developed with dry developer material comprising carrier granules having toner particles adhering triboelectrically thereto. The toner particles are attracted to the latent image, forming a visible powder image on the photoconductive surface. After the electrostatic latent image is developed with the toner particles, the toner powder image is transferred to a sheet. Thereafter the toner image is heated to permanently fuse it to the sheet.
It is highly desirable to use an electrostatographic reproduction machine of this type to produce color prints. In order to produce a color print, the electrostatographic reproduction machine includes a plurality of stations. Each station has a charging device for charging the photoconductive surface, an exposing device for selectively illuminating the charged portions of the photoconductive surface to record an electrostatic latent image thereon, and a developer unit for developing the electrostatic latent image with toner particles. Each developer unit deposits different color toner particles on the respective electrostatic latent image. The images are developed, at least partially, in superimposed registration with one another, to form a multicolor toner powder image.
The resultant multicolor power image is subsequently transferred to a sheet. The transferred multi-color image is then permanently fused to the sheet forming the color print. In both monochromatic and color systems the developer housing includes rotating components, such as magnetic rolls and augers, that are supported by bearings. These bearings must be kept free of developer material to ensure long developer housing life. Augers used to transport material in developer housings can push material towards bearings leading to premature bearing failures.
Some developer housings incorporate “pump auger” style shaft seals. These work by incorporating a directional screw thread on the rotating shaft which is in contact with a captive brush of developer material. The captive brush is created by a stationary surrounding ring magnet. The rotating screw threads actively push or “pump” material away from the bearing of the pump augers. This design has proven effective and shows increased life over just using a stationary ring magnet surrounding the rotating shaft. Unfortunately, some new developer designs must also run backwards for the purpose of dumping the developer material. There have been numerous bearing failures when pump auger seals were added to a developer housing that must periodically run backwards. When run backwards, the pump auger seals will pump material towards the bearing, leading to premature bearing failures.
At a development station, a development system or developer unit develops the latent image recorded on the photoconductive surface. A chamber in a developer housing stores a supply of developer material. To convey the developer material in the chamber to the latent image and to mix and triboelectrically charge the developer, a series of augers and magnetic rollers are strategically placed in the chamber and supported by the developer housing. Since these augers and rollers rotate, bearings are used to support the rollers at the housing.
The bearing is typically a sealed ball bearing having lip seal on both sides thereof. The auger is located in a chamber formed by a developer housing. The chamber contains developer material which is transported, agitated and mixed by the auger. The auger extends through an opening in the developer housing. The magnetic seal is located in the opening adjacent the chamber. The bearing is located adjacent an outer face of the developer housing. Magnetized carrier granules are magnetically attracted to the magnetic seal and form a barrier in the opening of the housing. If the bearing does not use grease, the lip seals may not be absolutely necessary. However, the magnetic seals are not completely effective in containing the toner or carrier. When vibrations and mechanical forces are present in the developer housing, the magnetic attraction of the beads to the magnet are not sufficient to overcome the vibrations and mechanical forces and toner or carrier beads will pass through the seal. U.S. Pat. No. 5,450,169 (Hart) discloses magnetic seals used in electrophotographic development stations. Hart is incorporated by reference into the disclosure of the present invention.